The invention pertains to detection, identification and analyses of gases. Particularly, it pertains to the detection of gases that indicate potential problems with equipment or the ambient environment. More particularly, the invention relates to health monitoring of the same.
Aspects of structures and processes related to gas detectors may be disclosed in U.S. Pat. No. 6,393,894, issued May 28, 2002, and entitled “Gas Sensor with Phased Heaters for Increased Sensitivity,” which is incorporated herein by reference, and in U.S. Pat. No. 4,944,035, issued Jul. 24, 1990, and entitled “Measurement of Thermal Conductivity and Specific Heat,” which is incorporated herein by reference.
The power industry relies on the operation of large, one to ten mega watt (MW) and 15,000 gallon or so oil-immersed electric power distribution transformers, of which there are about 100,000 installed in the United States and about 400,000 in the rest of the world. These transformers cost between one-half and five million dollars and thus amount to an installed base of around 200 billion dollars. Their design lifetime is forty to fifty years; their average life is presently about thirty-five years. The transformers are failing at the rate of about one percent per year. Unexpected failures of the transformers have cost utilities upwards of about eighteen million dollars.
However, it is far too expensive for utilities to replace all this aging equipment at once. So there is great interest in monitoring the “health” of the equipment so that any equipment susceptible to failure can be detected, watched and/or repaired or replaced. The potential multi-million damage, electric service interruption and financial cost resulting from unanticipated failure of utility-power transformers make it necessary to monitor the state of their “health”. Such monitoring is being suggested and presently being implemented via labor-intensive periodic off-line or high-capital-cost on-line analysis of the tell-tale changes in the composition and concentration of gases appearing in the transformer oil and in its head-space.
The “fault gases” in the insulating oil or in the head space of the transformer may provide an early indication of transformer failure. Fault gases are produced by high voltage breakdown in oil-filled transformers. Analysis of the dissolved gases in oil or in the head-space of a transformer has shown that they include acetylene (C2H2), methane (CH4), ethane (C2H6), carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), oxygen (O2) and ethylene (C2H4). The gas composition is indicative of the type of impending transformer failure and is the reason that low-cost, single gas monitoring does not provide a very high percentage of fault coverage. Detection and analysis of very small amounts of such gases in an inexpensive, efficient and inexpensive manner is desired.